Microwave power divider



J. F. ZALESKI ET AL 2,769,145

MICROWAVE POWER DIVIDER Oct. 30, 1956 2 Shee ts-Sheet 1 Filed Aug. 1.0,1951 J F. ZALESKI -r AL 2,769,145 MICROWAVE POWER DIVIDER United StatesPatent 2,769,145 MICROWAVE POWER DIVIDER Application August 10, 195 1,Serial No. 241,222 5 Claims. (Cl. 333-4) This invention pertains to anadjustable microwave power divider, and more specifically to a devicefor variably coupling a source of microwave energy to one or more branchutilization circuits while presenting a substantially constant impedanceto the source. a

i In controlling large amounts of microwave energy, the need arises forcontinuously varying the power output of a microwave generator or othersource between zero and a maximum value while maintaining constantoutput impedance. It is highly desirable that this should be done so asto present a constant impedance to the generator and, for convenience,should .be effected by the continuous adjustment of a simple controlmeans. The prior conventional devices employed for low power control,that is, for outputs of less than about watts of average power or 1kilowatt of pulse power, are not applicable, and the conventional highpower attenuators that are known are:.not readily adjustable. 1

The instant invention provides a device for apportioning microwaveenergy in a wave guide between a plurality of output branches, some ofwhich may comprise dissipative loads. It is easily and continuouslyadjustable, and causes substantially no reflection, so that voltagestanding wave ratios under. 1.05 are obtainable.

The device is essentially an adjustable, constant-impedance energydivider having in general at least two microwave output branches. Ifdesired one branch may contain an absorption load while others areconnected to utilization devices constituting useful loads. Thus byvariation of the adjustment of the device the output to the useful loadscan be continuously varied from zero to the full capacity of thegenerator or source. Since the device of the instant invention is apower divider, it can not only be used for the above purpose but alsocan be used for adjustably dividing a quantity of input power in anydesired ratio between a plurality of useful loads, with no substantialvariation in the impedance of the load imposed upon the generator orsource.

As will be clearer from subsequent description the socalled branchwaveguides, coupling irises and other electrical equivalents, throughwhich microwave energy is transferred from one guide to anothercorrespond to the two conductors of circuits for currents havingfrequencies below the microwave range, and therefore such irises orwaveguides may be considered to be the equivalent of terminal pairs inthe lower frequency field.

One purpose of the instant invention is to provide an improved devicefor controlling the flow of microwave energy from a microwave sourcewhile at the same time presenting a constant impedance to the source.

Another purpose of the instant invention is to provide a constantimpedance means for dividing a quantity of microwave energy adjustablyinto at le ast two portions having any selected ratio.

One embodiment of the invention chosen for purposes of illustrationcomprises a hollow round microwave guide having at least two rectangularcoupling irises mm H Patented Oct. 30, 1956 "ice stituting outputterminals in the walls of the guide connecting with respective outputhollow microwave guides. The functioning of the apparatus includes theexcitation within the round guide of the TE1,r mode of microwavetransmission. The principles of operation basically depend upon thecontrolled relative rotational position of the electromagnetic fieldwithin the round guide with respect to the position of the couplingirises by which variable energy coupling is provided between theelectromagnetic field in the round waveguide and the branches connectedto the coupling irises. The coupling irises are disposed substantiallyapart around the axis of the round guide so that there are reciprocaltrigonometric function relationships between the coupling of theelectromagnetic field in the round guide with the respective branches.The elimination of reflections. that would cause losses and variationsof impedance loading of the source is effected by conventional means,and any dummy load employed may be of any known type.

A better understanding of the invention will be obtained by reference tothe detailed description and the drawings in which:

Figure 1 illustrates one form of the present invention comprising around hollow wave guide having a shunt rectangular guide side connectionand two rectangular guide end connections, one rotatable.

Figure 2 illustrates a second embodiment comprising a round hollow waveguide having a series rectangular guide rotatable side connection andtwo rectangular guide end connections.

Figure 3 illustrates a third embodiment of the present invention.

Referring now to Fig. 1 a rectangular hollow wave guide 11 constitutesmeans for introducing microwave energy to a microwave energy divider ofthe present invention. As regards the present invention the output endof the waveguide 11 where it connects to the disc 12 can be consideredthe source of microwave energy, be it a generator or a waveguideenergized from a generator. The internal width and breadth of waveguidessuitable for the conduction of microwave energy of any specific wavelength in a particular mode are Well known in the art, and as anexample, the rectangular guide. 11 and all others in the embodiments ofthis invention are specified as having internal width and height of 0.9inch and 0.4 inch, respectively, suitable for the transmission of the3.3 cm. or X-band of microwave energy. When the Wave guide 11 has thesedimensions, X-band microwaves are transmitted only in the dominant TEL!)mode. It is to be understood that this invention is applicable to anylength of microwave providing, of course, that the components have theappropriate dimensions for the frequencies.

The rectangular guide 11 terminates in a closely fitaperture or couplingiris in a metallic disc 12 that constitutes the end of a round hollowwave guide 13. The junction between the rectangular wave guide 11 andthe round wave guide 13 is matched by suitable devices to prevent adiscontinuity that wouldreflect energy back into the guide 11. Asuitable matching device consists of inductive vanes, which will bedescribed later It is well known that the dominant TE1,0 mode in arectangular guide corresponds to the dominant mode TE1,1 of a round waveguide. By definition, the dominant mode is the one with the longestcutofi wave length. Accordingly, the dominant mode in a rectangularguide is determined and fixed relative to the inner surface of the guideby the relation of the wavelength and the dimensions of the waveguide.In a rectangular waveguide the position of the transverse electricalfield of the TE1,0 mode is parallel with the direction of the narrowerdimension. On the other hand, in a round waveguide all points on theinner surface with the dominant with guide 13, is rotatable. In orderthe guide 11 may be connected to a source of microwave energy (notshown) by a conventional flexible rectangular guide, or, alternatively,a microwave generating device, such as a klystron tube or a magnetronmay be fixed to the guide 11 l0 The two rectangular wave guides 26positioned and 27 are so apart around When this orientation exists thereis pedance.

a minimum im- 30 When the junction between the guides 16 and electricfield is parallel to the broad 'faces, no microwave energy enters therectangular guide 26 and all is reflected as though the disc 28 wassolid. This is the case when the relative orientation of the guide 11and guide 26' is as depicted in Fig. 1; in order to reduce to a minimumthe impedance at the coupling iris 29, 31 between the end of the guide16 and the guide '26, the latter would have to be rotated 90 in'eitherdirection.

between the waveguides be true, the distance A between the electricalcenter of the guide 27 and the end plate 28 must be one-fourth of a wavelength in the guide, or

Ag T. t y a This is because it is necessary that all microwave energyarriving at the guide 26 and not accepted thereby because of theorientation thereof, and hence reflected by the end 28, must return tothe guide 27 so as to be in phase with energy approaching at the sameinstant from the guide 11. This condition exists only when the distanceis as specified or is an odd integral multiple M thereof, expressed asThe energy-dividing action of the apparatus described may be moreclearly understood when it is considered that the E vector of the TE1,1mode induced in the round guides 13, 16 by the TE1,o mode of therectangular guide 11, is along a diameter of the round guides and mayberesolved into two voltage vectors along any two mutually perpendiculardirections in a plane perpendicular to the axis of the guides 13 and 16.The values of each of these vectors will be proportional to the cosine,of the angle it makes with the resultant. These vectors then willrepresent the proportions of voltage received by the guides 26 and 27 asthe input guide 11 is rotated relative to the guide 16. The energyreceived by each of the guides 26 and 27 will be proportional to thesquares of the respective voltages, and their sum will equal the inputenergy. In all cases the eifect of the variation of the impedance of thetotal load upon the generator, as observed from the generator, or theinput end of guide 11 will be substantially zero, usually less than 1%.This is one of the salient features of this invention.

It is obvious that if the arm 11 be fixed and the round guide 16together with its output arms 26 and 27 be rotatable, it will benecessary in general to make connections to the arms 26 and 27 byflexible guide or equivalent means. i The output arms26 and 27 may beconnected respec- 'tively to two useful respective loads, or aspreviously mentioned, one may be connected to a useful load, such as atransmitting antenna, while the other may be connected to a dummy loadof any known type suitable for the amount of powerto be dissipated. Inthis case either the arm 26 or the arm 27 may be connected to the usefulload, as the characteristics of the output arms 26 and 27 are quitesimilar.

Since operationally, the arms 26 and 27 are rsimilar,.it is obvious thatthe end arm 26 may be replaced by a shunt side outlet of rectangularwaveguide identical to the guide 27 and located like it a distance of orodd multiple thereof, from the end plate 28, which should be solid andWithout any aperture. The replacing arm would be positioned 90mechanical degrees from the arm 27 around the round guide axis in eitherdirection, and the description of its operation would be similar to thatgiven for the case of the end and side outlet arms.

Referring now to Fig. 2, a round waveguide 32 is connected by means oftwo rotary joints 33 and 34, similar to the rotary joint 14, Fig. 1, totwo round wave guides 36 and 37 respectively, the guides 36, 37 may beof a size suitable for the transmission of a microwave in the TE1,1mode; for example, inch in diameter for X-band microwaves of 3.3 cm. inlength. The round guides 36 and 37 are terminated by metal disc ends 38and 39, to which are connected rectangular wave guides 41 and 42 ofdimensions suitable for supporting the TE1,0 mode of the X-band. Thebroad sides of the respective guides 41 and 42 are oriented at rightangles with respect to each other and are mechanically connected by anysuitable means so as to be rotated together around their common axis,this connection being schematically indicated by the dashed line 43. Theround guide 32 has a series side arm 44 consisting of a rectangular waveguide of a size suit- Nxg for reasons which will presently appear.Theoretically, the use of a series side arm can be made the electricalequivalent of a shunt side arm by appropriately changing the dimensionsB and C.

In this embodiment the side arm 44 is adapted to serve as an input formicrowave energy and the end arms 41 and 42 are adapted as outputterminals. Energy entering the round guide 32 from the rectangularseries side arm guide 44 divides, with one-half passing toward the guide41 and the remainder toward the guide 42. The microwave energy in theround guides 32, 36 and 37 is transmitted by fields in the TE1,1 mode,these fields having, in a guide positioned as depicted in Fig. 2 their Evectors in the horizontal plane. The orientation of the E vectors isdetermined by the polarization of the rectangular input guide 44. Suchfields are accepted by rectangular guides oriented like guide 42because, as mentioned above, the dimensions of this guide are such as tosupport a TE1,u mode of the X-band which mode corresponds to the TE1,1mode of the round guide. Accordingly, the guide 42 presents a minimumimpedance to the microwave energy in round guide 32 of the polari zationmentioned while guide 41 presents a maximum impedance as if the roundguide end 38 were solid. The distance B being equal to NXg 2 thereflected energy is returned to the location of the guide 44 at suchphase as to reinforce waves travelling toward the right, so that all ofthe energy introduced at the guide 44 is received by the guide 42. l

By similar reasoning, it is readily seen that if the guides 41 and 42 beturned about the axis of the round guide 32 through an angle of all ofthe energy will be emitted from the guide 41 and none from the guide 42.Likewise, at intermediate positions of the guides 41, 42 the energytransmitted by each guide will be a function of the angle between thebroad faces of the respective guides 41, 42 and the E vector in roundguide 32, which vector is fixed by the position of guide 44 as describedin connection with Fig. 1. In all cases the substantial constancy of theimpedance of the device as reflected to the generator or input terminal44 is of the greatest practical utility.

It is obvious that in place of either or both output terminal guides 41and 42 there may be substituted side arm output rectangular guides,either of the shunt type 27, described in connection with Fig. 1, or ofthe series type identical with the input arm 44, Fig. 2. In either casethe adjacent round guide ends may be solid and the distances between theends and the respective output side arms would be i for the shunt typeand i for the series type.

As a further corollary, more than two outlets may be provided with themicrowave energy dividing in accordance with the principles described,to the outlets in accordance with the respective orientation of theoutlets with respectto the polarization of the field in the round guide.I

In Fig. 3 a TE1,1 field is excited in a inch diameter round guide 46 bythe introduction through an end plate 47 of microwave energy in theTE1,0 mode from a rectangular waveguide 48, the field in the round guide46 being rotatable through rotation of the input guide 48 and the endplate 47 relative to the, round guide 46. R- tat-ional movement betweenthe waveguide 48 and the round guide 46 is permitted by the provision ofa connecting rotary joint 49 which is similar in construction to joint14 shown in Fig. l. A side outlet terminal in the form of rectangularguide 52 is provided. So far the power divider is similar to thatdescribed in connection with Fig. 1. However, in Fig. 3 the end outputterminal 50 is of the circular cylinder guide type and consists of anabsorptive load. This dummy load may be of any one of a number of knowntypes suitable for the power required to be dissipated and in the formshown is a wood cone 51 having a resistive skin of colloidal graphite..The apex of the cone is pointed toward the power input and is longenough to prevent the effect of 'a discontinuity that would causereflections. Its length in any case should not be less than one andone-half times the diameter of its base.

The rectangular guide shunt side arm 52 is positioned at a convenientdistance from the input end 47. Since the round guide 46 is notreflective at its loaded end 50, a reflective, quarter-wave closed stub53 is provided to 'cause proper functioning of the side arm 52. Thisstub 53 is of the shunt type and is positioned on the round guide 46 inlongitudinal alignment with the arm 52, on the side away from the powerinput guide terminal 48. The electrical distance D between theelectrical center of the stub 53 and the electrical center of the arm 52must be or an odd multiple thereof in instances, both where the shuntand series types of arms and stubs are used.

A mode transformer 55 is provided to permit all input and outputbranches of the complete device to remain stationary, and yet providefor the adjustable rotation of the guide 48 about the axis of the powerdivider to vary the orientation of the field within the guide 46 withrelation to the side outlet terminal arm 52. The mode transformer 55consists of two round guides 54 and 56 connected by a rotary joint 57similar to that described in, connection with Fig. l. The guides 54 and56 have an internal diameter of 1 inches and are closed by respectivesolid metal disc ends 58 and 59. An input branch or terminal in the formof a rectangular guide 61 connected to the guide 54 as a series side armis positioned a distance G, equal to one-half of a TMo,1 mode wavelengthand of a. TE1,1 mode wavelength in the guide from the disc end 58, andan output branch in the form of a rectangular guide 62, also connectedto the guide 56 as a series side arm, is positioned a distance F equalto one-half of a TMo,1 mode (a of a TE mode wavelength) in the guidefrom the disc end 59. An orientation scale 63 fixed to the guide 56 isassociated with a fixed index plate 64 to determine the relativeposition of the guide. 56 and the guide 54. The output terminal 62 isconnected by a length of curved rectangular waveguide 66 to therotatable input waveguide 48 of the power divider. 7

In the operation of this modified form the input terminal61 may be fixedto a microwave generator, or

other input equipment, and the output terminal 52 may be fixed tostationary output or utilization equipment. The part between the rotaryjoint 57 and the rotary joint 49 may be rotatably adjusted and itsorientation is indicated by the position of the scale 63 attached to theround guide 56 in relation to the index mark 67 carried by the fixedindex plate 64.

The specific diameters of the guides 54 and 56 are such as to supportboth the TMo,1 mode and the TE1,1 of propagation of microwave energy onein resonance and the other in anti-resonance therein. The introductionof microwave energy in the TE1,o mode through the rectangular guide 61to the round guide 54 tends to cause both modes TE1,1 and TMo,1 to beestablished in the round guide 54 and 56. However, because the distanceGis 2 of TMo,1 mode and TE1,1 mode (resonant to TMo,1 and anti-resonantto TE1,1), the TE1,1 mode may be said to be tuned out, and itselimination leaves the mode TMo,1 as the sole means of propagation ofall of the input energy without reflection through the guides 54 and 56to the rectangular output'guide 62 where the transformation to theTE1,1) mode recurs without harmful reflection because of the terminationof the round guide 56 by the end plate 59 at the particular distance Ffrom the longitudinal center of the rectangular guide 62. The TMo,1 modesolely existing in the round guides 54 and 56 is symmetrical about theaxis of the guides, so that the relative axial rotation of the guides 54and 56 causes no change whatever in the phase or orientation of themicrowave energy entering the branch or terminal 62. This energy is delivered to the terminal 48 without substantial loss or reflectionregardless of its angular position. The angular position of the terminal48 does determine, however, the orientation of the TE1,1 mode in theround guide 46 and therefore determines the division of energy betweenthe output arm 52 and the dummy load 51, in exactly the way that fieldorientation determines energy division in the'embodirnent described inconnection with Fig. 1.

As a result, the mode transformer 55 provides the means for carrying outthe purposes of this invention yet obviates the necessity for employingflexible guides or other adjustable coupling attachments to the inputand output end terminals. The impedance of the load on the generator (orother source) remains constant for all orientations of the rotatableportion of the device, a fact of the greatest utility.

It is obvious that the mode transformer 55 of Fig. 3 can be applied toany input or output microwave terminal connection in the end of a roundguide that may be required in any of the embodiments of this invention.It is also obvious that the side arm and end arm input and outputterminal connections and all other components described may beassociated in a great many combinations, but in most cases each of suchcomponents and each of their interrelations should preferably be as havebeen herein described in connection with the embodiments of theinvention.

Within the broad aspects of the present invention the rectangularguides, may be considered as polarizing irises and it will be clearlyunderstood by those skilled in the art that the rectangular guides couldbe replaced by other intenconnecting waveguides or coaxial lines so longas they are capable of transmitting the desired frequencies. Theimportant thing is that either the interconnecting device or thecoupling device be capable of polarizing or of being sensitive toelectric fields of a definite polarization. Also the mode transformer 55interposed between the input 61 and output terminal 52 in Fig. 3 may beconsidered merely illustrative of a component for transmitting orcarrying circularly polarized microwave energy at the desired frequency.

Any of the rectangular guide input and output arms or terminalsdescribed in the example can be replaced by any other well-known deviceby which the TE1,1 mode can be induced in a round guide, or which can beexcited by the TE1,1 mode in a round guide while being sensitive to theorientation of the electric field thereof. Common examples of suchwell-known devices include an antenna or probe extending a suitabledistance into the side wall of a round guide, and a side or end apertureof generally elongated shape. Any of such devices may be employed so asto be electrically the equivalent of the described rectangular waveguide input and output arms. Each of the side arms and other branchguides by which the microwave energy is transmitted correspondseffectively to the two conductors of an electrical circuit forfrequencies below the microwave region. Accordingly, for convenience,the word terminal is used in such sense in the appended claims and inthe specification.

What is claimed is:

1. A microwave power controlling device comprising a waveguide sectioncapable of supporting independently at orthogonal positions in saidsection only the dominant TEu non-circular mode of wave transmission ata given frequency, said section having an impedance discontinuity forreflecting wave energy in at least one plane of polarization, inputmeans for establishing incident wave energy in said non-circular mode insaid section with the transverse electric vector at a selected plane ofpolarization, a plurality of output means connected to said section atposition orthogonally related electrically around the axis of saidsection, at least one of said output means being connected at anin-phase position for incident and reflected wave energy, said outputmeans being connected to said section through respective oblongpolarizing coupling apertures having their planes of polarizationorthogonally related, the major axes of said apertures being of suchdimension as to support only the dominant TEio mode corresponding to theTE11 mode in said section, the minor axes of said apertures being ofsuch dimension as not to support a dominant mode corresponding to theTEro mode in said section and means for changing the plane ofpolarization of the incident wave relative to said polarizing outputcoupling apertures.

2. A microwave power controlling device comprising a hollow waveguidesection capable of supporting independently at orthogonal positions insaid section only the dominant TEu non-circular mode of wavetransmission at a given frequency, said section having one endterminated in an impedance for reflecting wave energy in at least oneplane, input means for establishing incident wave energy in saidnon-circular mode in said section with the transverse electric vector ata selected plane of polarization, a first output means connected to saidterminated end of said round section, a second output means connected tothe side of said first section at an in-phase position for incident andreflected wave energy reflected from said terminated end of saidsection, said output means being connected to said section throughrespective oblong polarizing coupling apertures orthogonally relatedelectrically about the axis of said section, the major axes of saidapertures being of such dimension as to support only the dominant TE1omode corresponding to the TE11 mode in said section, the minor axes ofsaid apertures being of such dimension as not to support a dominant modecorresponding to the TEio mode in said section and means for changingthe plane of polarization of the incident wave relative to saidpolarizing output coupling apertures.

3. An adjustable microwave power controlling device comprising a roundhollow waveguide section having such internal diameter as to supportonly the TEii mode of wave transmission at a given frequency, apolarizing oblong input guide rotatably attached in coaxial relation toone end of said round section, the other end of said round sectionhaving terminating means: for reflecting wave energy in at least oneplane, a first hollow polarizing oblong output arm coupled in coaxialrelation to the other end of said round section at a fixed orientationtherewith to accept microwave energy in a plane of polarizationorthogonal to that reflected by said terminating means, a second hollowoblong polarizing output arm connected to the side of said round guideat an in-phase position along the axis of said round section with itsplane of polarization orthogonally related about the axis of said roundsection to the plane of polarization of said first output arm, the majoraxes of said oblong guides being of such dimension as to support onlythe dominant TEIO mode corresponding to the TEM mode in said roundsection, the minor axes of said arms being of such dimension as not tosupport a dominant mode corresponding to the TE10 mode in said sectionand means for rotating said input arm about its axis whereby the waveenergy entering said round section through said oblong input arm will bedivided between said output arms as functions of the angular position ofE vector in said round section with respect to the respective planes ofpolarization of the respective output arms.

4. An adjustable microwave power controlling device comprising a roundhollow waveguide section having such internal diameter as to supportonly the TE11 mode of wave transmission at a given frequency, saidsection having its ends terminated in impedances for reflecting waveenergy in respective orthogonal planes, an input arm fixed to one sideof said section and coupled through a polarizing aperture, a pluralityof output means connected to said round section through respectiverotatably adjustable walls having polarizing coupling apertures, :saidoutput arms being connected to said round section at in-phase positionsspaced along the axis of said round section, the major axes of saidapertures being of such dimension as to support only the TEm modecorresponding to the TEii mode in said section, the minor axes of saidapertures being of such dimension as not to support the dominant mode insaid section, means connecting said rotatably adjustable walls forrotating them in unison about the axis of said round guide whilemaintaining the major axes of said output apertures in a relativelyfixed orthogonal relation, whereby the wave energy in the TE11 mode insaid round section will be divided between said output arms asrespective functions of the position of the E vector in said roundsection with respect to the respective planes of polarization of theTE1o mode in the respective output arms without substantially affectingthe total impedance at said input arm.

5. An adjustable microwave power controlling device comprising a roundhollow waveguide section having such internal diameter as to supportonly the TEu mode of wave transmission at a given frequency, saidsection being terminated in an impedance for reflecting wave energy inone plane, a rectangular input arm and a plurality of rectangular outputarms connected to said round section, said input arm being fixed to theside of said round section with its axis perpendicular to the axis ofsaid round section, the broad walls of said input arm beingperpendicular to the axis of said round section, the broad walls of saidoutput arms being parallel to the axis of said round section andperpendicular to each other, said output arms being rotatably connectedto the opposite ends of said round section, means for simultaneouslyrotating said output arms in unison about the axis of said round guidewhile maintaining their orthogonal relation to each other, said outputarms being connected to said round section at in-phase positions alongthe axis of said round section whereby wave energy in said round sectionwill be divided between said output arms as functions of the respectiveReferences Cited in the file of this patent UNITED STATES PATENTS2,129,712 Southworth Sept. 13, 1938 Regan:

12 Bowen Oct. 7, 1941 Ring Aug. 12, 1947 Fox Mar. 23, 1948 Dicke Aug. 5,1952 OTHER REFERENCES Microwave Transmission Circuits, vol. 9,

M. I. T. Rad. Lab. Series, published by McGraw-H-ill, pages 368-69. Copyin Patent Office Library.

